Effects of low-cycle fatigue on bending properties and fracture toughness of un-HIP'ed Ti-47Al-2Cr-2Nb-1B intermetallic

Ingots of γ-TiAl base intermetallic alloy were cast in a metallic mould preheated at three different temperatures in order to obtain three different near-fully-lamellar microstructures. Four-point bending strength, bending strain to fracture, fracture toughness, hardness and low cycle bending fatigue strength (σmax)L of near-fully-lamellar Ti-47Al-2Cr-2Nb-1B with different colony sizes and interlamellar spacings were measured on un-HIP'ed test bars. The effects of low-cycle fatigue, 2×105 alternate bending cycles (R=0.1), at high stress intensity levels, i.e. the fatigue limit, on mechanical behaviour of the three different microstructures were evaluated. The data reported and discussed in this paper show that bending fatigue “training” enhances the mechanical behaviour of this material, mainly through the appearance of a plastic deformation during the bending test. The effects of the microstructures on bending deformation, fracture behaviour and fatigue resistance were discussed as well.